# Circuit to test a 30ua Moving Coil Meter

#### mendipviews

Joined Sep 27, 2020
2
Struggling to build a circuit to test a 30ua Moving Coil Meter properly
Any Pointers

Many Thanks
Luke

#### AlbertHall

Joined Jun 4, 2014
10,419
A power supply and a resistor. Measure the voltage across the resistor, calculate the current and compare with the meter reading.

#### dl324

Joined Mar 30, 2015
11,587
Welcome to AAC!

30uA is the current for full scale deflection. If you don't have a current source that low, you could install a shunt across the meter so it will take a larger current for full scale deflection.

#### AlbertHall

Joined Jun 4, 2014
10,419
you could install a shunt across the meter so it will take a larger current for full scale deflection.
To get an accurate shunt value you need to know the meter coil resistance.

#### mendipviews

Joined Sep 27, 2020
2
Thanks for the replies
I was thinking of testing the movement with a resistor in series from a 1.5v battery but can't get the math to add up properly.
Meter Resistance is 3250ohms. Its quite a rare movement so don't want to kill it

#### dl324

Joined Mar 30, 2015
11,587
I was thinking of testing the movement with a resistor in series from a 1.5v battery but can't get the math to add up properly.
Meter Resistance is 3250ohms. Its quite a rare movement so don't want to kill it
Go for half scale deflection or less to start:
$$R=\frac{V}{I}=\frac{1.5V}{15uA}=100k\Omega$$

Using a 100k resistor in series would give you slightly less than half scale deflection.
$$I=\frac{V}{R}=\frac{1.5V}{103,250\Omega}=14.5uA$$

#### vu2nan

Joined Sep 11, 2014
162
It would be easy, using an analogue multimeter. In the resistance measuring ranges the multiplier and the test current would be marked. With the required range selected, and with the prods on the terminals of the meter under test (negative prod on positive terminal and vice versa), it should read the test current and the multimeter its coil resistance.